Posterior Pituitary

What is the posterior pituitary?

The posterior pituitary is the back lobe of your pituitary gland, which is a small, pea-sized gland located at the base of your brain below your hypothalamus.

Your pituitary gland is made of two lobes: the anterior (front) lobe and posterior (back) lobe. Your pituitary gland is a part of your endocrine system. The posterior pituitary stores and releases just two of the many hormones your pituitary gland is responsible for: oxytocin and antidiuretic hormone (ADH, or vasopressin).

What is the pituitary gland?

Your pituitary gland is a small gland located at the base of your brain below your hypothalamus. It’s a part of your endocrine system and is in charge of making many different important hormones. Your pituitary gland also tells other endocrine system glands to release hormones.

Your pituitary gland is connected to your hypothalamus through a stalk of blood vessels and nerves. This is called the pituitary stalk. Through the stalk, your hypothalamus communicates with your pituitary gland and tells it to release certain hormones. Your hypothalamus is the part of your brain that controls functions like blood pressure, heart rate, body temperature and digestion.

The pituitary gland makes the following hormones:

• Adrenocorticotropic hormone (ACTH or corticotropin).
• Antidiuretic hormone (ADH, or vasopressin).
• Follicle-stimulating hormone (FSH).
• Growth hormone (GH).
• Luteinizing hormone (LH).
• Oxytocin.
• Prolactin.
• Thyroid-stimulating hormone (TSH).

What is the endocrine system?

Your endocrine system is a network of several glands that create and secrete (release) hormones.

A gland is an organ that makes one or more substances, such as hormones, digestive juices, sweat or tears. Endocrine glands release hormones directly into the bloodstream.

Hormones are chemicals that coordinate different functions in your body by carrying messages through your blood to your organs, skin, muscles and other tissues. These signals tell your body what to do and when to do it.

The following organs and glands make up your endocrine system:

• Hypothalamus.
• Pituitary gland.
• Thyroid.
• Parathyroid glands.
• Adrenal glands.
• Pineal gland.
• Pancreas.
• Ovaries.
• Testes.

What hormones are secreted by the posterior pituitary?

The posterior lobe of the pituitary gland stores and releases (secretes) only two hormones:

• Antidiuretic hormone (ADH, or vasopressin): ADH helps regulate the water balance in your body by controlling the amount of water your kidneys reabsorb while they’re filtering wastes out of your blood.
• Oxytocin: In people assigned female at birth (AFAB), oxytocin helps labor to progress by contracting the uterus, causes breast milk to flow and influences the bonding between parent and baby. In people assigned male at birth (AMAB), oxytocin can also influence the bonding between parent and baby and plays a part in ejaculation — oxytocin contracts the vas deferens to push sperm and semen forward for ejection.

Your hypothalamus actually produces these hormones, but your posterior pituitary stores them and releases them.

What does the posterior pituitary do?

The main role of the posterior pituitary is to store and releases two hormones: oxytocin and antidiuretic hormone (ADH, or vasopressin).

Both of the lobes of your pituitary gland are connected to your hypothalamus (a part of your brain) through a stalk that contains blood vessels and nerve cells. Your hypothalamus makes oxytocin and ADH and then tells your posterior pituitary when to store and release them by sending nerve signals through the pituitary stalk.

How does the posterior pituitary interact with other organs and glands?

Your posterior pituitary interacts directly with your hypothalamus since your hypothalamus creates oxytocin and antidiuretic hormone (ADH, or vasopressin) and sends signals to your posterior pituitary about when to store and release the hormones.

Oxytocin interacts with and affects the uterus, mammary glands and vas deferens. ADH interacts with and affects your kidneys

Where is the posterior pituitary located?

Your pituitary gland is located at the base of your brain, behind the bridge of your nose and directly below your hypothalamus. It sits in an indent in the sphenoid bone called the sella turcica.

Your pituitary gland is made of two lobes that touch each other. The posterior pituitary is the back lobe of your pituitary gland, meaning it is facing the back of your head, whereas the anterior pituitary is in the front and is facing the front of your head.

How big is the posterior pituitary?

Your pituitary gland is only about 1/3 of an inch in diameter in total — about the size of a pea. The posterior pituitary is smaller than the anterior pituitary. The anterior pituitary makes up about 80% of the total weight of your pituitary gland.

What are the common conditions and disorders that affect the posterior pituitary?

The main issues related to the posterior pituitary are hypersecretion (too much) of oxytocin or antidiuretic hormone (ADH, or vasopressin) and hyposecretion (too little) of oxytocin or ADH.

Most of these conditions are rare. Tumors can also affect your posterior pituitary, but they are also rare. Pituitary tumors more commonly affect the anterior lobe of your pituitary gland.

Hyposecretion of antidiuretic hormone (ADH, or vasopressin)

Hyposecretion of antidiuretic hormone (ADH, or vasopressin) happens when there’s a decrease in either the production of ADH in your hypothalamus or the release of ADH from your pituitary gland. It’s usually caused by damage to your hypothalamus or posterior pituitary and, in rare cases, by a gene mutation (change). In some cases, the cause is unknown.

Having lower-than-normal amounts of ADH prevents your kidneys from reabsorbing water, so it’s released in your urine. This makes your urine very diluted (watery) and your blood very concentrated.

A lack of ADH can cause a rare water metabolism disorder called central diabetes insipidus (CDI). It's not to be confused with — and is not related to — diabetes mellitus, which happens when your body doesn't produce or properly use insulin. CDI can become life-threatening if it’s not treated.

Symptoms and side effects of diabetes insipidus include:

• Frequent urination (polyuria).
• Extreme thirst (polydipsia).
• Fatigue (due to having to wake up several times overnight to pee).
• Dehydration.

Hypersecretion of antidiuretic hormone (ADH, or vasopressin)

Hypersecretion of antidiuretic hormone (ADH, or vasopressin) happens when there’s an increase in either the production of ADH in your hypothalamus or the release of ADH from your posterior pituitary. When this happens, it’s called the syndrome of inappropriate antidiuretic hormone secretion (SIADH). Having excess amounts of ADH causes your body to retain too much water. This makes your urine very concentrated and your blood overly saturated with water (diluted).

There are several causes of SIADH and excess ADH levels. Some more common causes include:

• Certain medications, such as certain Type 2 diabetes medications and anti-seizure medications.
• Having surgery under general anesthesia.
• Brain conditions, such as injury, infections and stroke.
• Brain surgery in the region of your hypothalamus.

Symptoms of excess ADH levels are most often caused by having low sodium levels in your blood. Symptoms of having a low blood sodium level include:

• Nausea and vomiting.
• Headache.
• Problems with balance that may result in falls
• Mental changes, such as confusion and memory problems.

Hyposecretion of oxytocin

Hyposecretion (too little secretion) of oxytocin is rare. Having lower-than-normal levels of oxytocin stop uterine contractions and milk ejection during the birthing process. Although it’s rare, the most common cause of lower-than-normal oxytocin levels is a condition called panhypopituitarism, a condition in which all pituitary gland hormone levels are below normal.

Hypersecretion of oxytocin

Hypersecretion (too much secretion) of oxytocin is very rare and is called oxytocin toxicity. Higher-than-normal levels of oxytocin result in an overactive uterus, causing an increase in uterine muscle mass (hypertrophy), which limits pregnancy due to there not being enough space in the uterus to hold the fetus.

Are there tests that can check the health of my posterior pituitary?

If you’re experiencing symptoms related to posterior thyroid issues, your healthcare provider may order tests to check your levels of antidiuretic hormone (ADH, or vasopressin) and/or oxytocin.

An antidiuretic hormone (ADH) blood test can help detect, diagnose and determine the cause of ADH deficiency and excess.

Your levels of oxytocin can be tested with several different fluids, including spit (saliva), blood, plasma, urine and cerebrospinal fluid.

If your test results come back abnormal, your provider may suggest having an imaging test such as an MRI (magnetic resonance imaging) to take a look at your pituitary gland.

When should I see my doctor?

If you’re experiencing any symptoms of central diabetes insipidus (CDI) or syndrome of inappropriate antidiuretic hormone secretion (SIADH), contact your healthcare provider.

A note from Cleveland Clinic

Most health issues related to disorders of your posterior pituitary are rare. If you experience new or concerning symptoms, it’s important to talk to your healthcare provider. They can usually run some simple tests to assess your health.